EXTRACTING MESSAGES MASKED BY CHAOS

We show how to extract messages that are masked by a chaotic signal in a system of two Lorenz oscillators. This mask removal is done for two different modes of transmission: a digital one, where a parameter of the sender is switched between two values, and an analog mode, where a small amplitude message is added to the carrier signal. We achieve this without using a second Lorenz oscillator as a receiver, and without doing a full reconstruction of the dynamics. This method is robust with respect to transformations that impede the unmasking using a Lorenz receiver, and is not affected by the broadband noise that is inherent to the synchronization process. We also discuss the limitations of this way of extraction for messages in high frequency bands. © 1995 The American Physical Society.